We're working on accepting Bitcoin through Coinbase, just wasn't quite ready for this tee!
"Green address" means whitelisting addresses from the big online wallet sites because you trust them not to launch double-spending attacks against you. Coinbase would also be a great green address provider.
Shoot me an email (in my profile) if you need a beta tester!
Also can you please please please get American Apparel 50/50 shirts? They're the only shirts I buy now.